2.1. Prevalence of dentofacial deformities

There are no exact epidemiologic data of dentofacial deformities in adult populations, but Proffit and White (1991) estimated, on the basis of United States Public Health Service studies from the 1960’s, that the prevalence of skeletal Class II malocclusions in the USA population was roughly 10%, about 3% of which were severe enough and at the right age to warrant surgery, mostly (70%) mandibular surgery. The corresponding figures for skeletal Class III malocclusions were 0.6% and 21%, and for severe open bite 0.6% and 16%. Recently, Proffit et al. (1998) gathered malocclusion data from the National Health and Nutrition Examination Survey (NHANES III) in the USA and found approximately 20% of the US population to have deviations from the ideal bite, and 2% of these were severe enough to be disfiguring and at the limit for orthodontic correction capacity. In this study, the prevalence of severe Class II malocclusions (defined as > 6 mm overjet) was found to be 4.3% in the age groups of 18–50 years, while that of Class III malocclusions (defined as ≥ 3 mm overjet) was 0.3%. In Scandinavia such information is mainly available for children: malocclusion frequencies of approximately 40% to 75%, or even higher, have been reported (Heikinheimo 1989, Permert et al. 1998), and 10% of young people would be in definite need for (orthodontic) treatment. In the Netherlands, a nationwide survey showed that Angle Class II dental relation was present in 28% and maxillary overjet of more than 5 mm in 23% of the population. An objective need for orthodontic treatment was recognized in 39% of the population (Burgersdijk L et al. 1991). If the data from the USA (Proffit & White 1991) are adjusted to Finland, although recalling that populations differ from each other in many aspects, there would be 510 000 people with skeletal Class II, approximately 15 000 of whom would need surgery, and 30 600 and 6400 subjects with Class III, correspondingly. According to the more recent approximation of Proffit et al. (1998), a million Finns (20%) would have deviations from ideal bite, and 20 000 (2%) of them would be in need of surgery. Since approximately 400 orthognathic operations are performed in Finland annually, it would take 50 years to operate these patients, assuming that no new malocclusions would appear in the meantime. Therefore, these scores seem quite high as far as the treatment resources and costs are concerned and are based solely on morphologic deviations. There also exists a controversy as to the definition of malocclusion and the indicators for treatment (Heikinheimo 1989). However, other relevant factors apart from purely anatomical ones, such as psychosocial and biophysiological, also affect the need and demand for treatment.